The Origin of Species - Chapter 24

 

Two Concepts of Species

• Morphospecies- Organisms with very similar physical form
  • Splitters- Break apart species into new ones on the basis of small phenotype changes
  • Lumpers- Group many phenotype variants into one species
• Biological Species
  • A group of organisms that could interbreed in nature and produce fertile offspring
  • Organisms do not have to only be similar to each other. (Hill)

 

Other Definitions of Species

 

Palentological species concept- this approach is based on the fossil record.  It is similar to the morphological species concept, except that it is based on the similarity of extinct species bodies.  This is the only way we can classify extinct species, as we don’t know about their mating behaviors.  (Evan Johnson)

 

Keller, Amy.  "Chapter 24: The Origin of Species."  Avon High School.  Avon, IN.  8 December 2008.

 

Ecological species concept- this approach is based on how a species interacts with its environment or its niche.  For example, two species may look similar but can be differentiated by what food they consume.  This approach works for both sexual and asexual species.  (Evan Johnson)

 

Keller, Amy.  "Chapter 24: The Origin of Species."  Avon High School.  Avon, IN.  8 December 2008.

 

Phylogenic species concept- this approach defines a species as a group of organisms with a special genetic history; like a “branch” on the tree of life.  This approach uses molecular biology in comparing animals.  It is frequently used to denote small differences in “sister species”.  (Evan Johnson_

 

Keller, Amy.  "Chapter 24: The Origin of Species."  Avon High School.  Avon, IN.  8 December 2008.

 

Recognition Species Concept-Species are defined by the ability of the individuals in the population to recognize certain characteristics in each other.

Cohesion Species Concept- Emphasizes cohesion of phenotypes (complex of genes and set of adaptations)

Evolutionary Species Concept- Emphasizes evolutionary lineages and ecological roles. 

(Fernandez)

 

Requirements for Speciation

Speciation- The origin of new species in evolution.  This requires three things in order to ocurr:

1.  Variation in the population

2.  Selection

3.  Isolation

(Keller)

All of these need to be happening for speciation to ocurr.  (Griesenauer)

 

Keller, Amy.  "Chapter 24: The Origin of Species."  Avon High School.  Avon, IN.  8 December 2008.

 

Reproductive Barriers

Reproductive barriers- The existence of biological factors (barriers) that impede members of two species from producing viable, fertile hybrids (Cambell and Reece 473).  They also preserve the genetic integrity of a biological species (maintain a species).  A single barrier may not block all genetic exchange, but a combination of several will isolate a species' gene pool.  There are two main types that are described below:     (Griesenauer)

 

Keller, Amy.  "Chapter 24: The Origin of Species."  Avon High School.  Avon, IN.  8 December 2008.

 

Prezygotic Barriers- prevent mating or fertilization, before the formation of a zygote by preventing mating between species or successful fertilization should gametes meet.

• Habitat Isolation- two species in same area but occupy different habitats
• Behavioral Isolation- courtship is different
• Temporal Isolation- different breeding seasons (or in like flowers open in different time of day)
• Mechanical Isolation-The two species are physically unable to mate. (Archibald) the Chewa-wa and the German Shepherd, it just aint’ happinin
• Gametic Isolation- gametes fail to fuse together. Causes can be that the sperm cannot survive in the female reproductive tract of females of the other species, or the sperm cannot penetrate the protective lair of the female’s egg. (Archibald)  

 

Postzygotic Barriers- prevent offspring from being fertile.

• Reduced Hybrid Viability- zygote does not survive embryonic development
• Reduced Hybrid Fertility- baby is born just sterile
• Hybrid Breakdown- offspring is okay, but their offspring are feeble or sterile

 

Introgression

• transfer of alleles between two species, but only a partial gene flow.
• result-some intermixing of genes between two species.
• a possible mechanism for gene flow between similar species.

(Fernandez)

 

Allopatric Speciation

• When geography cuts off gene flow between two subpopulations
• Earthquake creates a gorge, or Atlantic and Pacific ocean animals separated by Panama

• The division of the two species can range from the widest oceans to the distance between two drops of water. (Archibald)

• Can result in new species

 

Sympatric Speciation

• Reproductive barriers prevent gene flow between overlapping populations

 

http://www.pandasthumb.org/pt-archives/allopatry.jpg

(Fernandez)

 

http://www.pandasthumb.org/pt-archives/Sympatry.jpg

(Fernandez) 

 

 

Gradualism Evolution

• Small, gradual change over an extended period of time (Darwin)
• Fossils should show continuous links, which creates a problem because their are missing links in our fossil record

 

Punctuated Evolution

• Elridge and Gould 1972
• Punctuated Equilibrium
  • Long periods of stasis are punctuated by episodes of relatively rapid speciation and change
  • Two speeds slow and the rapid bursts
• Speciation can  then occur over a short span of time (1 to 1,000 years)
• Fossil record will then have gaps
• This is the latest and greatest explanation of evolution 

 

(Wilcoxson) 

 

Adaptive Radiation

Adaptive radiation is the introduction of new environment and challenges. This is common when organisms wonder into unfamiliar areas, or distant journeys. This is how many species become extinct and survival becomes very tough. (Brandt)

 

Long-distance dispersal is a type of adaptive radiation in which nature disperses an organism, and then the organism adapts differently to each environment.  An example is when seeds from a plant stick in the feathers of a bird and are then carried for a long distance to another environment and then fall off, and evolution begins in the new environment. (Harris)

 

Anagenesis is the accumulation of heritable changes over time changing the appearance of an organism.

Cladogenesis is the branching evolution in which a new species is formed from an existing species with while the parent generation remains the same or similar. (Ryan)

 

Homeotic genes – determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a plant’s flow parts are arranged. (Harris)

 

Campbell, Neil A., and Reece, Jane B. AP Edition Biology. 7th. San Francisco: Pearson Benjamin Cummings, 2005.

 

Hox Genes – product of one type of homeotic genes which provide positional information in an animal embryo.  Evolutionary changes such as the evolution from invertebrates to vertebrates are associated with alterations in Hox Genes and the genes that regulate them. (Harris)

 

Evolution of Genes That Control Development (AWAN)

     Changes in Timing and Rate

          -heterochrony: an evolutionary change in the rate or timing of developmental events. ex: organisms shape depends on growth rate of different body parts

.         -allometric growth: proportion that helps give a body its specific form. Ex: different rates of allometric patterns contribute tio the contrasting shapes of humans.

          - paedomorphosis: reproductive development accelerates compared to somatic development, the sexually mature stage of species may retain features that were juvenile strucures. (Awan)

    

     Campbell, Neil A., and Reece, Jane B. AP EDITION BIOLOGY. 7th. San Francisco: pearson Benjamin Cummins, 2005.

 

Species selection – a theory maintaining that species living the longest and generating the greatest number of species determine the direction of major evolutionary trends. (Harris)

 

 

Review Questions

1. The type of evolution that results in the greatest increase in biological diversity is:

a. anagenesis

b. cladogenesis

c. phyletic evolution

d. microevolution

e. both a and c are correct.

(Fernandez)

 

2. Which of the following is not a type of intrinsic reproductive isolation?

a. mechanical isolation

b. behavioral isolation

c. geographic isolation

d. gametic isolation

e. temporal isolation

(Fernandez)

 

3. Two species of frogs occasionally mate, but the offspring do not complete development.  What type of barrier isolates these gene pools?

a. gametic isolation

b. prezygotic barrier

c. hybrid breakdown

d. reduced hybrid viability

e. reduced hybrid fertility

(Fernandez)

 

4. For which of the following is the biological species concept least appropiate?

a. plants

b. animals

c. bacteria

d. fossils

e. both c and d

(Fernandez)

 

ANSWERS: 1. b, 2. c, 3. d, 4. e

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Works Cited 

          Keller, Amy.  "Chapter 24: Origin of Species."  Avon High School.  Avon, IN.  8-10 December 2008.

 

          Taylor, Martha R.. Student Study Guide for Biology. 7th. San Francisco, CA: Pearson Benjamin Cummings, 2005.